Nonreciprocal rectangular wave guide device



Feb. 5, 1963 W. H. HEWITT. JR

NONRECIPROCAL. RECTANGULAR WAVE GUIDE DEVICE Filed June 17, 1953 2Sheets-Sheet l AT TENUA T/ON FIG. 2

FERRITE POSITIVE CIRCULAR POLAR/ZAT/ON NEGATIVE CIRCULAR POLARIZATION HRES. 5 TEAD r MAGNE TIC F/EL 0 lNl/ENTOR w H HE W/ TZI/n.

A 7' TORNE V Feb. 5, 1963 w. H. HEWITT, JR 3,

NONRECIPROCAL RECTANGULAR WAVE GUIDE DEVICE Filed June 17, 1953 l 2Sheets-Sheet 2 FIG. 4 a2 63 553%? our ur 6/ 64 I MICROWAVE SOURCE /62FIG. 6 67 I CENTERL/NE a5 OF 420 MIL WAVEGUIDE a: Q 75 s I as S k q 55 3E 45 v; 35

'5 I l I I LOCATION OF m/vs WAVEGUIDE (M/LS) INVE N 70/? 14 HHEW/77,1111

A TTOPNEV United States Patent Ofitice 3,076,946 Patented Feb. 5, 19633,076,946 NONRECIPROCAL RECTANGULAR WAVE GUIDE DEVICE William H. Hewitt,Jr., Mendham, NJ., assignor to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Filed June 17,1953, Ser. No. 362,191 6 Claims. (Cl. 333-242.)

This invention relates to very high frequency and microwave components,and more specifically to passive devices which have differenttransmission characteristics for opposite directions of transmission.

As developed in C. L. Hogans article entitled The Microwave Gyratorwhich appeared in volume 31, pages I through 31 of the January 1952 BellSystem Technical Journal, passive non-reciprocal microwave componentscan be obtained by the use of ferrite cylinders having an axial magneticfield in a circular wave guide. The gyrator structure disclosed in thisarticle, however, is a moderately complex structure, requiringtransition elements for changing from rectangular to circular wave guideand vice versa, resistive vanes for suppressing unwanted reflectedenergy and tapered impedance matching elements for the ferrite cylinder,for example.

Accordingly, a principal object of the present invention is to simplifynon-reciprocal microwave components.

A further object is to provide means for obtaining nonreciprocal effectsin wave guides of rectangular crosssection.

A still further object is to obtain non-reciprocal effects in waveguides with a minimum of gyromagnetic material, the material being sopositioned in the guide as to produce the desired result mosteffectively.

In accordance with the invention it is disclosed that an electromagneticwave guiding structure having a polarized element of gyromagneticmaterial located asymmetrically With respect to the electromagneticfield within the wave guiding structure has a different transferimpedance for one relative orientation of the radio frequency andpolarizing magnetic fields than for the opposite relative orientation.In one specific embodiment illustrated in the drawings, by way ofexample, a transversely magnetized septum of ferrite located off-centerin a rectangular wave guide is found to produce substantially greaterattenuation with the polarizing magnetic field in one direction thanwhen the polarizing field is reversed.

Other features, objects and advantages of the invention will becomeapparent during the course of the following detailed description of thespecific illustrative embodiments of the invention shown in theaccompanying drawings.

In the drawings:

FIG. 1 indicates the pattern of radio frequency magnetic loops of a TEdominant mode wave in a rectangular wave guide having a septum offerrite located therein;

FIG. 2 shows a cross-sectional view of a polarized septum of ferritelocated asymmetrically in a rectangular wave guide;

FIG. 3 is a plot showing two attenuation characteristics illustratingthe difference in attenuation when the septum of ferrite is located in aportion of the wave guide in of the magnetic intensity of the wave.

which positively or negatively circularly polarized magnetic waves arepresent, respectively;

FIGS. 4 and 5 are various views of a wave guide section similar to thatof FIG. 2 wherein the septum of gyromagnetic material is movabletransversely in the guide;

FIG. 6 shows a pair of plots of attenuation versus septum position forthe device of FIGS. 4 and 5 with oppositely polarized biasing magneticfields, respectively;

FIG. 7 is a block diagram of a simple microwave system in which theisolator of FIG. 2 is employed; and

FIG. 8 illustrates the principles of the invention as applied to adielectric wave guiding structure.

FIG. 1 indicates, by way of example and for purposes of illustration,the magnetic field configuration at a particular instant of a travelingelectromagnetic wave of the TE dominant mode being propagated from leftto right in rectangular wave guide section 11. The lines of magneticintensity are indicated by the loops 12, 13, 14, and lie entirely inplanes which are parallel to the wide dimension of the wave guide. As iswell known to those skilled in the art, at points on vertical lines suchas A-A and B-B, between the center line of the wave guide and eitherside wall, the magnetic field will have both longitudinal and transversemagnetic field components. The field at these locations may therefore besaid to be circularly or elliptically polarized, the direction ofcircular polarization being predominantly clockwise on one side (thenear side) of the center line and counterclockwise on the other side.This clockwise and counterclockwise polarization may be appreciated, forexample, by considering the directionof the lines of magnetic intensityat the fixed points 15 and 16 within the wave guide section 11 as themagnetic loops 12, 13 and 14 move along the guide from left to right.For a more complete discussion of the propagation of the dominant modeTE wave in a rectangular wave guide, see Principles and Applications ofWaveguide Transmission, by Dr. G. C. Southworth, published by D. VanNostrand Company, Inc., New York, 1950, with particular reference toSection 5.2 starting at page 102 and FIG. 5.2-1 on page 103. The taperedseptum 21 of paramagnetic material in the wave guide 11 will bediscussed in greater detail in conjunction with FIG. 2.

FIG. 2 shows a cross-sectional view of the wave guide 11 and a polarizedvertically transverse septum of ferrite 21. The polarizing field isapplied to the septum 21 by an electromagnet comprising the core 22 ofmagnetic material and the coil 23 when the coil 23 i energized by powerfrom a suitable electrical source 24 of direct current. A variableresistance 25 and the double pole double throw switch 26 provide foradjusting the strength of the magnetizing field and for reversing thesame, respectively.

As indicated by D. Polder, Philosophic Magazine, v01- ume 40, pages 99through 115, January 1949, the permeability of an extended ferritemedium for an electromagnetic wave whose magnetic intensity is at rightangles to a steady biasing magnetic field is substantially different foroppositely circularly polarized components One physical explanationwhich has been advanced to explain this phenomenon involves theassumption that the ferromagnetic material contains unpaired electronspins which tend to line up with the applied magnetic field. Theseelectron spins and their associated moments can be made to precess aboutthe line of the magnetic field, keeping an essentially constantcomponent of magnetic moment in the biasing magnetic field direction butproviding a magnetic moment which may rotate in a plane normal to thissteady magnetic field direction. These magnetic moments have a tendencyto precess in one angular sense, bu strongly resist rotation in theopposite sense. This tendency of a spinning element to consistentlyprecess in one angular direction to the exclusion of the other isfamiliar to anyone who has watched a top wobble before stopping.Considering the interaction between the oppositely polarized componentsof high frequency magnetic intensity and the magnetic moments, it isclear that one of the circularly polarized components will be rotatingin the easy angular direction of precession of the magnetic moments andthe other component will be rt-ating in the opposite direction. When thehigh frequency magnetic intensity is rotating in the same sense as thepreferred direction for precession of the magnetic moment, it willcouple strongly with the magnetic moment and drive it into precession.When the high frequency magnetic intensity is rotating in the oppositeangular direction, however, very little coupling or interaction betweenthe high frequency magnetic intensity and the magnetic moment takesplace.

Furthermore, while this difference in coupling and consequent differentin permeability for oppositely polarized components is not limited toparticular values of frequency or magnetic field strength, certainparticularly useful effects are observable at resonance. Referring toMG. 3, for example, plots 28 and 2 9 of the attenuation (whichcorresponds closely to the imaginary portion of the permeability) forthe respective positive and negative circularly polarized components ofa high frequency magnetic'field versus biasing magnetic field for aferrite medium are shown. From this plot it may be observed that whenthe natural resonance frequency of the magnetic moment as determined bythe strength of the applied field coincides with the driving frequencyof the high frequency magnetic field components circularly polarized inthe preferred sense, a large amount of power can be absorbed from thedriving field. However, very little power is absorbed from theoppositely circularly polarized component.

The element 21 of FIG. 2 is made from a paramagnetic material which haslow conductivity. Any of a number of ferromagnetic materials which eachcomprise an iron. oxide in combination with one or more bivalent metals,such as nickel, magnesium, zinc, manganese or other similar materialhave proved to be satisfactory. Thesematerials combine with the ironoxide in a spinel structure and'are known as ferromagnetic spinels or aspolycrystalline ferrites. In accordance with the usual practice, thesematerials are first powdered and then molded with a small percentage ofplastic material such as Teflon or polystyrene. As a specific example,the element 21 may be a strip of nickel-zinc ferrite of the approximatechemical formula (Ni Zn )Fe O prepared as noted above. In addition,commercially available samples .of ferrite, and finely powderedconducting ferromagneticdust in an insulating binder may be employed. Byway of inclusion but not of limitation, the phrase paramagnetic materialhaving low conductivity is to be construed as applying to the foregoingtypes of materials; In addition, as employed in the present applicationand claims, the term gyromagnetic medium is intended to apply to allmaterials having magnetic properties of the type disclosed in theabove-mentioned-article by Folder, and as discussed above in conjunctionwith FIG. 2.

FIG. 4 illustrates a wave guide unit which was actually employed todemonstrate the phenomena discussed in the present specification. ThisWave guide component comprises a section of wave guide 31, ofrectangular cross-sectionhaving a broader cross-sectional dimension asshown in FIG. 4 and a narrower cross-sectional dimension substantiallyone-half the broader dimension, equipped with conventional couplingelements 32 and 33 at its ends, respectively, and a ferrite vane orseptum 34. Vane '34 may be adjusted transversely in the wave guide by amicrometer-controlled mounting, as shown, and is located centrallybetween the ends of the section of wave guide 31.

In more detail, the element of ferrite 34 is mounted on the threaded endof rod 36 of low dielectric constant material by means of the two nuts45 and 46. The rod and ferrite vane are maintained in their properangular orien tation by the pin 37 which is secured to the rod 36 andwhich is restrained from rotation by the slot 33 in the housing 39. Thevane 34 is moved by rotating the knob 41 which is threaded to thehousing 39 and is coupled for longitudinal motion with the rod 36. Theposition of the vane 34 within the guide 31 may be determined from thevernier calibrations 42, 43 on the knob 41 and the housing 39,respectively. Intermediate the ends of the wave guide section 31 andopposite the end of rod 36, a removable element 44- is provided to giveaccess to the plastic nut 45 which holds the vane 34 against the othernut 46 and onto the rod 36. With the element 44 removed, nut 45 and vane34 may be removed and a different vane may be inserted from one end ofthe wave guide and mounted on rod 36, so that measurements with varioustypes and shapes of vanes may be made. The structure 43 shown in dottedlines is a flange which holds'the housing 39 and the wave guide 31together.

FIG. 5 is an enlarged cross-sectional view taken along the lineindicated at 5-5 of FIG. 4. The section is taken parallel to thenarrower side wall of the wave guide and shows the tapered vane orseptum of ferrite 3d and the nut 45.

In FIG. 6, the results of a set of measurements using the device of H68.4 and 5 are shown graphically. in this set of measurements, the vane orseptum 34 was formed of a ferrite having a resistivity of ohmcentimeters and had a chemical composition (Zn MnQFe O The frequency ofthe electromagnetic waves was 23,725 megacycles, and the vane or septum34 was magnetized to ferromagnetic resonance for the characteristics ofcurves 52 and 53. The plot 51 was obtained with no biasing magneticfield, the plot 52 was obtained with a transverse biasing field of 4,470oersteds in one direction, and the plot 53 was obtained with a biasingfield of 4,250 oersteds in the opposite sense. It is believed that aslight anisotropy in the internal magnetic field of the sample causedthe difference in biasing magnetic fields required for resonance and theresultant slight difference in attenuation peaks. It should be notedthat only the central portion of the wave guide is shown in FIG. 6.Specifically, the wave guide is 420 mils wide and the center line of thewave guide section falls at mils on the scale used in this PEG. 6. Whilethe values of attenuation indicated in the plot of FIG. 6 are ratherhigh, it is to be understood that with other samples, similarcharacteristics having lower levels of attenuation may be readilyobtained. One way in which this can be accomplished is by reducing theconcentration of paramagnetic material either by using a thinner vane orby using a higher proportion of dielectric binder to paramagneticmaterial.

It may be observed from the plots of FIG. 6 that the maximum differencein attenuation for the oppositely directed biasing fields obtains whenthe paramagnetic elements are located substantiallyoff-center in thewave guide but still fairly close to the center of the guide.Specifically when the term substantially off-center is employed in thepresent specification and claims, this signifies that the center of theparamagnetic septum is at least 1 or 2 percent of the distance from thecenter of the wave guide toward one wall.

FIG. 7 is a block diagram illustrating a typical application-ofanisolator in accordance with theinvention. In

this case, the microwavesources 61 and 62 feed the same output circuit63 and it is desired that no microwave energy be coupled from source 62into source 61. An isolator 64 in accordance with FIG. 2 is accordinglyplaced between the sources 61 and 62. This isolator,

when a suitable biasing magnetic field is applied thereto,

effectively blocks transmission from microwave source 62 to source 61 asindicated by point 66 on line 67 of FIG. 6, while allowing a substantialamount of transmission in the opposite direction, as indicated by point68 on line 67 of this same FIG. 6. When the double pole double throwswitch 26 of FIG. 2 is reversed, however, the directions of easytransmission and effective isolation would, .of course, be reversed.From the schematic showing of FIG. 7, it is evident that isolators inaccordance with the present invention would be useful to preventfrequency pulling of a microwave source by reflections from an impedancediscontinuity such as is frequently presented by an antenna.

FIG. 8 illustrates the principles of the invention as applied to adielectric Wave guide of the type disclosed in A. G. Fox applicationSerial No. 274,313, filed March 1, 1952, now Patent 2,794,959, grantedJune 4, 1957. As shown in FIG. 8, the wave guiding structure comprisesan elongated element of dielectric material 71, which has onecross-sectional dimension substantially greater than the other in orderto maintain proper electromagnetic field orientation. The transverselypolarized strip of ferrite 72 which is embedded off-center in thedielectric wave guide 71 serves the same isolation purpose for thedielectric wave guide 71 as the element 21 of FIG. 2 does for the waveguide 11. This paramagnetic element 72 may be permanently magnetized orbe magnetized by a suitable electromagnet spaced from the wave guide 71and having a core of low conductivity paramagnetic material, so as notto distort that portion of the field pattern which is external to theguide. It may be noted that the transverse magnetization will againproduce the desired relationship of biasing magnetic field perpendicularto the circularly Polarized components of the high frequency magneticintensity.

It is to be understood that the above-described arrangements are simplyillustrative of the principles of the invention. Numerous otherarrangements using other known types of electromagnetic wave guidingstructures or employing gyromagnetic materials polarized at fieldstrengths other than at resonance may readily be devised by thoseskilled in the art, for example, without departing from the spirit andscope of the invention.

What is claimed is:

1. A device for modifying electromagnetic wave energy propagationcomprising a section of bounded wave guide having a boundary ofrectangular transverse cross-section and continuous conductivity, meansfor applying electromagnetic wave energy having a solely transverseelectric field pattern with a region of maximum electric intensity tosaid section, a longitudinally extending vane element of gyromagneticmaterial located within said section in the path of and in couplingrelationship with said energy, and means for applying a steady magneticfield to said gyromagnetic element, said element being disposedsubstantially asymmetrically in the transverse cross-section of saidwave guide section and centered in a region of electric intensitysubstantially less than said maximum by an amount suflicient tosubstantially enhance the modifying effect of said material upon thepropagation of said energy over that for said element centered in saidregion of maximum electric intensity.

2. In combination, a Wave guide structure having mutually perpendiculartransverse dimensions which are different, means for applying atraveling electromagnetic wave in a frequency range including a givenoperating frequency to said wave guide having a component of themagnetic field thereof extending in a first direction, a comparativelythin, flat, elongated element of gyromagnetic material which extendslongitudinally for at least a wavelength of said energy at saidoperating frequency located off center upon the larger transversedimension of said wave guide and in coupling relationship with respectto said traveling electromagnetic wave, means for applying a transversebiasing magnetic field to said gyromagnetic element in a seconddirection at right angles to said first direction so that said elementinfluences the propagation of said wave to a first extent, and means forapplying a selected one of said component field and said biasing fieldto said gyromagnetic element in a direction opposite from said firstnamed direction for said selected field so that the influence of saidelement is substantially different from said first extent.

3. A device for modifying electromagnetic wave energy propagationcomprising a section of bounded wave guide having a boundary ofrectangular transverse cross-section and continuous conductivity, meansfor applying to said section electromagnetic wave energy having a solelytransverse electric field pattern with a region of maximum electricintensity, a longitudinally extending vane of gyromagnetic materiallocated within said section in the path of and in coupling relationshipwith said energy, and means for applying a steady magnetic field to saidgyromagnetic vane in a direction parallel to the electric field lines ofsaid transverse electric field pattern, said vane being disposedsubstantially asymmetrically in the transverse cross-section of saidwave guide section and spaced from both narrow walls of said section andcentered in a region of electric intensity substantially less than saidmaximum by an amount sufficient to substantially enhance the modifyingeffect of said material upon the propagation of said energy over thatfor said vane centered in said region of maximum electric intensity.

4. In combination, a generally rectangular wave guide having a boundaryof continuous conductivity with broad and narrow walls, an elongatedvane of gyromagnetic material located off center toward one of saidnarrow walls within said wave guide, means for applying a travelingelectromagnetic wave to said Wave guide having a component of themagnetic field thereof extending in a first direction, means forapplying a transverse biasing magnetic field to said gyromagnetic vanein a second direction at right angles to said first direction wherebysaid vane influences the propagation of said wave to a first extent, andmeans for applying a selected one of said component field and saidbiasing field to said gyromagnetic vane in a direction opposite fromsaid first named direction for said selected field whereby the influenceof said vane is substantially different from said first extent.

5. A device for modifying electromagnetic wave energy propagationcomprising a section of bounded wave guide having a boundary ofrectangular transverse cross-section and continuous conductivity, meansfor applying electromagnetic wave energy having a solely transverseelectric field pattern with a region of maximum electric intensity tosaid section, a longitudinally extending vane element of gyromagneticmaterial located Within said section in the path of and in couplingrelationship with said energy, and means for applying a steady magneticfield to said gyromagnetic element in a direction parallel to theelectric field lines of said transverse electric field pattern, saidelement being disposed substantially asymmetrically in the transversecross-section of said wave guide section and centered in a region ofelectric intensity substantially less than said maximum by an amountsufficient to substantially enhance the modifying effect of saidmaterial upon the propagation of said energy over that for said elementcentered in said region of maximum electric intensity.

6. In combination, a wave guiding structure having a boundary ofrectangular transverse cross section and continuons conductivitycomprising pairs of opposed broad and narrow walls for support of wavesof dominant mode high frequency electromagnetic wave energy at theoperating frequency, and a vane of gyromagnetic material extendinglongitudinally within said structure in energy coupling relationshipwith the wave energy guided thereby, said vane being magneticallypolarized in a plane normal to the longitudinal extend of said vane andparallel to said narrow walls, said vane being located significantlyasymmetrically within the transverse cross-section of said structure andsymmetrically centered upon a line located between one narrow wall ofsaid structure and a plane parallel to said narrow walls containing thelongitudinal center line of said structure.

References Cited in the file'of this patent UNITED STATES PATENTS 82,745,069 Hewitt May 8, 1956 3,023,379 Turner Feb. 27, 1962 FOREIGNPATENTS 7 980,648 France Dec. 27, 1950 OTHER REFERENCES Kales, Chait,and Sakiotis: A Nonreciprocal Microwave Component, Journal of AppliedPhysics, vol. 24, No.6, June 1953, pages 816 and 817.

Hewitt: Microwave Resonance Absorption in Ferromagnetic Semiconductors,Physical Review, vol. 73, No. 9, 1948, pages 1118- 19.

Hogan: The Ferromagnetic Faraday Effect at Microwave Frequencies, BellTechnical Journal, vol. 31, January 1952, pages 1-31.

Beljers et al.: Gyromagnetic Phenomena Occurring with Ferrites, PhilipsTechnical Review, vol. 11, N0. 11, May 1950, pages 313-22.

NBS. Magnetic Attenuator, Technical News Bulletin Nat. Bureau ofStandards, August 1951, pages 110- 1 11.

5. A DEVICE FOR MODIFYING ELECTROMAGNETIC WAVE ENERGY PROPAGATIONCOMPRISING A SECTION OF BOUNDED WAVE GUIDE HAVING A BOUNDARY OFRECTANGULAR TRANSVERSE CROSS-SECTION AND CONTINUOUS CONDUCTIVITY, MEANSFOR APPLYING ELECTROMAGNETIC WAVE ENERGY HAVING A SOLELY TRANSVERSEELECTRIC FIELD PATTERN WITH A REGION OF MAXIMUM ELECTRIC INTENSITY TOSAID SECTION, A LONGITUDINALLY EXTENDING VANE ELEMENT OF GYROMAGNETICMATERIAL LOCATED WITHIN SAID SECTION IN THE PATH OF AND IN COUPLINGRELATIONSHIP WITH SAID ENERGY, AND MEANS FOR APPLYING A STEADY MAGNETICFIELD TO SAID GYROMAGNETIC ELEMENT IN A DIRECTION PARALLEL TO THEELECTRIC FIELD LINES OF SAID TRANSVERSE ELECTRIC FIELD PATTERN, SAIDELEMENT BEING DISPOSED SUBSTANTIALLY ASYMMETRICALLY IN THE TRANSVERSECROSS-SECTION OF SAID WAVE GUIDE SECTION AND CENTERED IN A REGION OFELECTRIC INTENSITY SUBSTANTIALLY LESS THAN SAID MAXIMUM BY AN AMOUNTSUFFICIENT TO SUBSTANTIALLY ENHANCE THE MODIFYING EFFECT OF SAIDMATERIAL UPON THE PROPAGATION OF SAID ENERGY OVER THAT FOR SAID ELEMENTCENTERED IN SAID REGION OF MAXIMUM ELECTRIC INTENSITY.